Fatal error: Uncaught Error: Call to undefined function set_current_screen() in /var/www/html/wp-admin/admin-header.php:30 Stack trace: #0 /var/www/html/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php(267): require_once() #1 /var/www/html/wp-content/plugins/civicrm/civicrm/CRM/Utils/System.php(219): CRM_Utils_System_Base->theme('<div id="crm-co...', false, false) #2 /var/www/html/wp-content/plugins/civicrm/civicrm/CRM/Core/Error.php(233): CRM_Utils_System::theme('<div id="crm-co...') #3 /var/www/html/wp-content/plugins/civicrm/civicrm/packages/PEAR.php(921): CRM_Core_Error::handle(Object(DB_Error)) #4 /var/www/html/wp-content/plugins/civicrm/civicrm/packages/DB.php(985): PEAR_Error->__construct('DB Error: alrea...', -5, 16, Array, 'CREATE TABLE ci...') #5 /var/www/html/wp-content/plugins/civicrm/civicrm/packages/PEAR.php(575): DB_Error->__construct(-5, 16, Array, 'CREATE TABLE ci...') #6 /var/www/html/wp-content/plugins/civicrm/civicrm/packages/PEAR.php(223): PEAR->_raiseError(Object(DB_mysqli), NULL, -5, 16, in /var/www/html/wp-admin/admin-header.php on line 30
Try adding following line in functions.php file of your child theme.
require_once(ABSPATH . 'wp-admin/includes/screen.php');
Which wordpress version and civicrm version are you trying?
It seems like you have two problems.
As Pradeep mentioned in the comments - it seems like your underlying error is that the install is trying to create a database that already exists. I can't tell for sure, because the error in #4 is cut off.
Additionally, there's the second error (undefined function) which is unfortunately WordPress-specific and I don't know the solution. However, completely removing/creating the CiviCRM database again (assuming that it's separate from WordPress) is likely to solve the first problem, and the second problem won't occur.